1. Field of the Invention
The present invention relates to a combustor capable of reducing NOx in a gas turbine.
2. Description of the Relevant Art
The entrance temperature of a gas turbine has been elevated in recent years to obtain higher efficiencies in cogenerator plants which tends to result in an increase in the generation of NOx. Serious demands for lower NOx content in the exhaust gases have thus been raised and met by various proposals.
One of the factors influencing-the amount of NOx produced is the combustion temperature, and it is known that the lower the combustion temperature the less NOx is generated. At present, therefore, a two-stage combustion system has been developed to effect efficient combustion and to suppress the rise of the combustion temperature and accordingly the generation of NOx. In this two-stage combustion system, diffusion combustion is performed at the first stage for obtaining ignition and flame stability, and premixed combustion is performed at the second stage to obtain a high NOx reducing effect.
FIG. 10 shows a premixed type of combustor for a gas turbine in the prior art. In FIG. 10, a gas turbine premixed type of combustor 01 has a pilot nozzle 02 at its center. A plurality of cylindrical main (or premixing) nozzles 03 are disposed along a common circle around the pilot nozzle 02. In this arrangement, each main nozzle 03 has its leading end located substantially in the same plane as that of the leading end of the pilot nozzle 02. Incidentally, reference numeral 04 designates a combustion chamber, and numeral 05 designates swirl vanes.
As described above, as the entrance temperature of the gas turbine rises, the more NOx is emitted to the atmosphere. This raises serious demands for a system producing a lower amount of NOx in the exhaust gases. Because the rise in gas temperature increases the amount of the air burnt, the mixing of the fuel and air is an important factor which has been investigated in reducing the NOx content of the exhaust gas.
In the premixed type of combustor of the prior art shown in FIG. 10, however, the premixing nozzles collectively constitute a cylindrical structure with the aim of achieving a compact combustor structure. Thus, the mixing of the fuel and air does not always sufficiently limit the generation of NOx.